Page 152 - DCAP508_DATABASE_ADMINISTRATION

Database Administration

Notes After a page has been updated, a read operation on the snapshot still accesses the original page,
which is now stored in a sparse file. The following figure illustrates a read operation on the
snapshot that accesses a page after it has been updated in the source database. The read operation
reads the original page from the sparse file of the snapshot.

Figure 10.15: Read Operation

Self Assessment

State true or false:
6. Database snapshots are independent on the source database

7. Database snapshots operate at the data-page level.
8. Taking regular backups and testing your restore plan are essential to protect a database.
9. The snapshots of a database must be on different server instance as the database.
10. To the user, a database snapshot appears never to change, because read operations on a
database snapshot always access the original data pages, regardless of where they reside.

10.4.3 Effect of the Update Pattern on Database Snapshot Growth

If your source database is fairly large and you are concerned about disk space usage, at some
point you should replace an old snapshot with a new snapshot. The ideal lifespan of a snapshot
depends on its growth rate and the disk space that is available to its sparse files. The disk space
required by a snapshot depends on how many different pages in the source database are updated
during the life of the snapshot. Therefore, if updates are mostly to a small subset of pages that
are updated repeatedly, the growth rate will slow over time and the snapshot space requirements
will remain relatively small. In contrast, when all of the original pages are eventually updated

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